1. Field of the Invention
The present invention relates to an optical disk apparatus for optically reproducing information recorded on a recording medium by utilizing a light beam from a light source such as a laser. In particular, the present invention relates to focus jumping control for moving a light beam spot from a recording/reproducing surface to another recording/reproducing surface on a recording medium having a plurality of recording/reproducing surfaces.
2. Description of the Related Art
In general, an optical disk apparatus conducts focus control by moving a converging lens in a direction substantially vertical to a recording/reproducing surface of a recording medium with a focus actuator. The focus actuator is composed of a movable part and a fixed part attached to a converging lens. The movable part and the fixed part are bound to each other via four wires or an elastic substance such as rubber. When an electric current flows through a coil provided in the movable part, an electromagnetic force is generated between the coil and a permanent magnet provided in the fixed part, thereby moving the converging lens in a direction substantially vertical to the recording/reproducing surface of the recording medium. The direction substantially vertical to the recording/reproducing surface refers to a vertical direction and a direction containing a slight deflection from the vertical direction. Furthermore, in the case where a recording/reproducing surface on which focus control currently is conducted is not a desired one, search for a desired information track on a recording medium having a plurality of recording/reproducing surfaces is conducted by repeating focus jumping to an adjacent recording/reproducing surface a plurality of times to conduct focus control on a desired recording/reproducing surface, and searching for a desired track.
Hereinafter, a conventional focus jumping method will be described in detail with reference to the drawings. FIG. 9 is a block diagram showing a schematic structure of a conventional optical disk apparatus that conducts focus jumping by a conventional focus jumping method. FIG. 9 shows a state of the optical disk apparatus during focus jumping. The conventional optical disk apparatus includes a disk motor 102 for rotating an optical disk 101 with two recording/reproducing surfaces (L0 surface, L1 surface) at a predetermined rotation speed, an optical head 103 (composed of a light source such as a semiconductor laser, a coupling lens, a polarized beam splitter, a polarizing plate, a converging lens, a condensing lens, a dividing mirror, a photodetector, and the like (not shown)) for reproducing information from the optical disk 101, and a traverse motor (not shown) for moving the entire optical head 103 in a direction vertical to a track of the optical disk 101.
A light beam generated by a light source is collimated by the coupling lens, reflected from the polarized beam splitter, passes through the polarizing plate, and is converged by the converging lens. In this manner, a light beam spot with a focus point in a thickness direction of the optical disk 101 is formed. The light beam spot is radiated to the optical disk 101 that is rotated by the disk motor 102. Light reflected from the optical disk 101 passes through the converging lens, the polarizing plate, the polarized beam splitter, and the condensing lens, and is split into light beams in two directions by the dividing mirror. One of the divided light beams is input to a focus control apparatus through a photodetector with a two-division structure. The focus control apparatus is composed of a focus error signal generating part 104, a digital signal processor (DSP) 901 as a focus control part, a focus driving circuit 111, and a focus actuator (not shown). The focus error signal generating part 104 is provided as a converged state detecting part for generating a signal corresponding to a converged state of a light beam. In the focus error signal generating part 104, an output signal from the two-division photodetector is input to a differential amplifier. An output signal from the differential amplifier becomes a positional shift signal (focus error (FE) signal) representing a shift between a converged point of a light beam and the optical disk 101, and is input to the DSP 901. The detection of the FE signal is called an xe2x80x9cSSD methodxe2x80x9d.
Focus control will be described. The FE signal input to the DSP 901 is converted from an analog signal to a digital signal by an AD converter 105, and is input to a compensating filter 107, which is a digital filter composed of an adder, a multiplier, and a delay circuit, through a switch 106. The compensating filter 107 compensates for a phase and the like of a focus control system. The FE signal with its phase compensated by the compensating filter 107 is input to an adder 109 through a gain switching circuit 108 that switches a loop gain of the focus control system. A switch 114 is turned off during focus control. Therefore, the FE signal passing through the gain switching circuit 108 passes through the adder 109 as it is, is converted from a digital signal to an analog signal by a DA converter 110, and is input to the focus driving circuit 111. The focus driving circuit 111 amplifies an output signal from the DSP 901 and converts its level in an appropriate manner, thereby driving the focus actuator. In this manner, the focus actuator is driven so that a light beam on the optical disk 101 takes a predetermined converged state, whereby focus control is realized.
On the other hand, the other light beam divided by the dividing mirror is input to a tracking control apparatus (not shown) via a photodetector with a four-division structure, which detects a signal representing a shift between a converged point of a light beam and a track on the optical disk 101, i.e., a track shift signal (tracking error (TE) signal) for controlling a converged point of a light beam to scan a track on the optical disk 101, and conducts tracking control based on the TE signal so that a converged point of a light beam scans a predetermined track on the optical disk 101. A structure and operation of the tracking control apparatus are not related to the description of the focus jumping method directly; therefore, the description thereof will be omitted.
The DSP 901 is provided with the switches 106 and 114. During focus control, the switch 106 is turned on, and the switch 114 is turned off. During focus jumping, the switch 106 is turned off, and the switch 114 is turned on. The switch 106 opens/closes a loop of the focus control system, and switches between an input signal during focus control and an input signal during focus jumping with respect to the compensating filter 107
Next, the focus jumping method will be described with reference to a waveform diagram in FIG. 10 and a flow chart in FIG. 11, as well as the block diagram in FIG. 9. FIG. 10 is a waveform diagram showing a FE signal and a focus driving waveform during focus jumping from the L0 layer to the L1 layer of the optical disk 101. During focus jumping from the L1 layer to the L0 layer, the polarity of the FE signal and the focus driving waveform become inverse to that of the waveforms shown in FIG. 10. Therefore, the waveform diagram and description thereof in this case will be omitted.
As is understood from the block diagram in FIG. 9, the switch 106 is turned off during focus jumping, and the compensating filter 107 is operated at an input zero. Therefore, the FE signal passing through the gain switching circuit 108 holds a low-pass component (surface deflection component) at the beginning of focus jumping. The adder 109 adds an acceleration/deceleration pulse signal generated in an acceleration/deceleration pulse generating part 113 to the low-pass component at the beginning of focus jumping, which has passed through the gain switching circuit 108. The addition signal drives the focus actuator, whereby the instability of focus jumping caused by surface deflection of the optical disk 101 is reduced.
First, at Step S1101, the switch 106 is turned off, and the switch 114 is turned on (set a position for focus jumping). At Step S1102, when an acceleration pulse (predetermined peak value Al) starts being output, the optical head 103 starts moving toward the L1 layer of the optical disk 101, and an FE signal in a sine wave is generated in accordance therewith. At Steps S1103 and S1104, an acceleration pulse is output for a predetermined period of time (T1), and the process waits until a zero crossing point (Z point in FIG. 10) of the FE signal is detected at Step S1105. The zero crossing point is detected by detecting a crossing point between the FE signal passing through the AD converter 105 and a predetermined level (zero in this case) in the level detecting part 112. At Step S1106, a deceleration pulse (predetermined peak value A2) starts being output. At Steps S1107 and S1108, a deceleration pulse is output for a predetermined period of time (T2). Thereafter, at Step S1109, the switch 106 is turned on, and the switch 114 is turned off (set at a position for focus control), whereby focus jumping to another recording/reproducing surface (e.g., from the L0 layer to the L1 layer) is completed, and focus control is restarted.
As described above, the conventional optical disk apparatus has a structure in which during focus jumping from a recording/reproducing surface to another recording/reproducing surface, a surface deflection component (shape of surface deflection) of the optical disk at the beginning of jumping is held, and a predetermined peak value, i.e., an acceleration/deceleration pulse are applied to the focus actuator for a predetermined period of time.
Herein, drawbacks of focus jumping in the case of reproducing information from an optical disk at a high speed by using the conventional optical disk apparatus will be described. In the case of reproducing information from an optical disk at a high speed, a ratio of focus jumping time to one rotation time of an optical disk is increased compared with the case of reproducing information from an optical disk at a low speed. Therefore, the position of surface deflection at the beginning of jumping substantially may be different from that at the end of jumping due to the influence of surface deflection of the optical disk. The above-mentioned conventional optical disk apparatus holds a surface deflection component at the beginning of jumping, and applies an acceleration/deceleration pulse to the surface deflection component. Therefore, during high-speed reproduction, the difference between the position a light beam reaches at the end of jumping and the position of surface deflection becomes remarkable, which makes focus jumping unstable.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an optical disk apparatus that is capable of conducting high-speed reproduction with stable focus jumping performance by storing a surface deflection component (a surface deflection shape) in one rotation of an optical disk and starting focus jumping in the case where a positional change of a surface deflection component during focus jumping is a predetermined value or less.
Another object of the present invention is to provide an optical disk apparatus that is capable of conducting high-speed reproduction with stable focus jumping performance by storing a surface deflection component in one rotation of an optical disk and updating the surface deflection component held at the beginning of jumping during focus jumping, using the stored values.
In order to achieve the above-mentioned objects, the optical disk apparatus of the present invention for reproducing information recorded on a recording medium includes: a moving part for moving a converged point of a light beam converged on a recording medium having a plurality of stacked recording/reproducing surfaces in a direction substantially vertical to the recording/reproducing surfaces; a converged state detecting part for generating a signal corresponding to a converged state of the light beam on the recording medium; a focus control part for driving the moving part in accordance with a focus error signal that is an output signal from the converged state detecting part, in such a manner that the light beam is converged at a substantially constant position on the recording medium; a focus jumping part for moving the converged point of the light beam from an arbitrary recording/reproducing surface of the recording medium to another recording/reproducing surface thereof; a surface deflection measuring part for measuring a shape of surface deflection of the recording medium; and a jumping starting part for operating the focus jumping part based on measurement results of the surface deflection measuring part.
Furthermore, the optical disk apparatus of the present invention includes: a moving part for moving a converged point of a light beam converged on a recording medium having a plurality of stacked recording/reproducing surfaces in a direction substantially vertical to the recording/reproducing surfaces; a converged state detecting part for generating a signal corresponding to a converged state of the light beam on the recording medium; a focus control part for driving the moving part in accordance with a focus error signal that is an output signal from the converged state detecting part, in such a manner that the light beam is converged at a substantially constant position on the recording medium; a focus jumping part for moving the converged point of the light beam from an arbitrary recording/reproducing surface of the recording medium to another recording/reproducing surface thereof; a surface deflection measuring part for measuring a shape of surface deflection of the recording medium; a surface deflection storing part for storing the measurement results of the surface deflection measuring part in a memory successively on a predetermined phase basis over one rotation of the recording medium; a converged position holding part for holding a converged position of the light beam at the beginning of focus jumping; and a surface deflection correcting part for updating the converged position of the light beam held by the converged position holding part during focus jumping, based on the stored values in the surface deflection storing part.
According to the above-mentioned structures, the optical disk apparatus of the present invention can store a surface deflection component in one rotation of an optical disk and start focus jumping in the case where a positional change in the surface deflection component during focus jumping to another recording/reproducing surface is a predetermined value or less. Because of this, an optical disk apparatus capable of conducting high-speed reproduction with stable focus jumping performance can be provided. It should be noted that a substantially vertical direction refers to a vertical direction and a direction containing a slight deflection from the vertical direction. It also should be noted that a substantially constant position of a light beam includes a slight deflection from a converged position.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.